Micturition Chapter 26: Anatomy of Urinary Bladder and Urethra

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Questions and Answers

What is the function of the detrusor muscle in the urinary bladder?

To stimulate the external sphincter

To increase the pressure in the bladder (correct)

To inhibit peristaltic contractions in the ureter

To relax the bladder

What is the location of the trigone in the urinary bladder?

On the anterior wall of the bladder

At the apex of the urethra

At the bladder neck

On the posterior wall of the bladder (correct)

What is the function of the internal sphincter in micturition?

To increase the pressure in the bladder

To stimulate the external sphincter

To prevent emptying of the bladder (correct)

To relax the bladder neck

What type of muscle is the external sphincter of the bladder?

Skeletal muscle Signup and view all the answers

What is the effect of parasympathetic innervation on the ureter?

Enhances peristaltic contractions Signup and view all the answers

What is the function of the sympathetic nervous system in the urinary bladder?

Stimulates blood vessels Signup and view all the answers

What is the function of the parasympathetic nervous system in the urinary bladder?

Detects the degree of stretch in the bladder wall Signup and view all the answers

What is the location of the external sphincter of the bladder?

In the urogenital diaphragm Signup and view all the answers

What type of fibers are involved in the somatic NS associated with the pudendal nerve?

Skeletal motor fibers Signup and view all the answers

What is the result of vesicoureteral reflux?

Increased pressure in the renal calyces Signup and view all the answers

What happens when a ureter becomes blocked?

Decreased urine output from the kidney Signup and view all the answers

What is the process of micturition?

The process of emptying the urinary bladder Signup and view all the answers

What are the two main steps of the micturition reflex?

Filling of the bladder and then contraction of the bladder Signup and view all the answers

What is the role of the cerebral cortex in the micturition reflex?

It facilitates or inhibits the micturition reflex Signup and view all the answers

What happens during voluntary urination?

The external urethral sphincter is inhibited Signup and view all the answers

What is the effect of sensory signals from the bladder stretch receptors?

They cause a further increase in reflex contraction of the bladder Signup and view all the answers

Study Notes

Anatomy of Urinary Bladder and Urethra

The detrusor muscle is a smooth muscle in the bladder that extends in all directions, increasing pressure in the bladder to 40-60 mm Hg when contracted.
The trigone is a small triangular area on the posterior wall of the bladder where the two ureters enter the bladder.
The internal sphincter is a smooth muscle that normally keeps the bladder neck and posterior urethra empty of urine, preventing bladder emptying until pressure rises above a critical threshold.
The external sphincter is a skeletal muscle under voluntary control, located in the urogenital diaphragm, and can consciously prevent urination.

Innervation of the Ureter and Urinary Bladder

The ureter is innervated by both parasympathetic and sympathetic nervous systems, enhancing and inhibiting peristaltic contractions, respectively.
The urinary bladder is innervated by:
Autonomic nervous system:
- Parasympathetic fibers (S2 and S3) detect bladder wall stretch and stimulate detrusor muscle contraction.
- Sympathetic fibers (L2) mainly stimulate blood vessels and have little effect on bladder contraction.
Somatic nervous system:
- Skeletal motor fibers through pudendal nerve control the external sphincter.

Vesicoureteral Reflux and Micturition Reflex

Vesicoureteral reflux occurs when bladder contraction during micturition does not completely occlude the ureter, leading to urine reflux into the ureter.
This can cause ureter enlargement, increased pressure in the renal calyces, and kidney damage.
The micturition reflex is an autonomic spinal cord reflex that empties the bladder when the tension in its walls rises above a threshold level.

Pain Sensation in the Ureters and Ureterorenal Reflex

Blockage of a ureter (e.g., by a stone) causes intense reflex constriction, severe pain, and sympathetic reflex back to the kidney, constricting renal arterioles and decreasing urine output.

Voluntary Urination

Voluntary urination involves contraction of abdominal muscles, increasing pressure in the bladder.
Sensory signals from bladder stretch receptors are conducted to sacral segments, reflexively causing contraction of the bladder and simultaneous inhibition of the external urethral sphincter.

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Description

This quiz covers the anatomy of the urinary bladder and urethra, including the detrusor muscle and trigone. Learn about the structure and functions of these important organs.